It’s officially the beginning of the end for life on Earth, researchers say.

Earth’s atmospheric carbon dioxide levels have passed 400 parts per million — long regarded as the point of no return in the battle against climate change.

Researchers at the Scripps Institution of Oceanography said the CO2 levels for September will definitely be above 400 ppm — a time when they typically record the lowest CO2 levels of the year. The findings come from Hawaii’s Mauna Loa Observatory, which has measured CO2 levels since 1958.

It’s hard to say exactly what this means — other than it’s nothing good — as humans have never existed with levels this high. The last time Earth surpassed 400 ppm was approximately 4 million years ago.

And even if the entire world stopped emitting CO2 tomorrow, it would take decades to erase the current levels.